Molding sand appropiate for the fabrication of cores and molds

ABSTRACT

The molding sand comprises hollow microspheres of aluminum silicate, preferably with an aluminum content between 15 and 45% by weight, a wall thickness between 3 and 10% of the particle diameter and a particle size between 10 and 350 μm. These sands are useful to manufacture low density cores with good “veining” and penetration characteristics, moreover maintaining the mechanical properties of the core obtained. These cores are useful in the manufacture of iron casting.

FIELD OF THE INVENTION

[0001] This invention is related to the manufacture of iron casting and,specifically, it refers to a molding sand for casting, suitable formanufacturing cores and chill molds, incorporating hollow microspheresof aluminum silicate.

BACKGROUND OF THE INVENTION

[0002] The iron casting obtained by using cores manufactured withmolding sand, generally have a series of defects in their shape, suchthat it is necessary to subject them to machining to obtain adimensionally correct piece. These defects are produced due to theheating the core suffers due to the effect of the molten metal pouredover it, provoking its expansion and hence, the appearance of fissureson its surface. The molten metal penetrates these fissures, henceforming a kind of partition wall or laminas on the surface of the pieceobtained. This undesired effect is known “veining” or “rat's tail”.

[0003] At present, the cores are manufactured using molding sands andgas- or heat-cured resins, or self-curing resins, together withadditives destined to improve the characteristics of the piece obtained.

[0004] To prevent the formation of “veining”, a series of techniques areknown and used, such as:

The Use of Iron Oxide as an Additive

[0005] The iron oxides used as additives, are destined to minimize theproblems created by the expansion of the silica contained in the sands,being used for such a purpose red, black, yellow iron oxides or ironoxide from Sierra Leone, which are incorporated to the mixture inpercentages varying from 1 to 3%. These oxides act as a factor for theformation of feyalite, such that the “veining” is minimized during theformation of the fissure. Nevertheless, this technique besides noteliminating “veining” in some cases, has as a disadvantage that the ironoxide reduces the mechanical resistance of the core and moreover theformation of feyalite increases the tendency to penetration, causing theexternal surface of the piece obtained to present irregularities, whichshould be treated later.

Use of Wood Flours and Coal Powder

[0006] According to this technique, wood flour or coal powders are addedin proportions varying from 1 to 3%. These flours burn during melting,hence leaving free gaps distributed throughout the volume of the core,permitting that the expansion of the silica is produced in these gapswithout the need to increase the external size, hence avoiding theappearance of fissures provoking “veining”. The main disadvantage ofthis technique is that when the flours burn, a large amount of gas isproduced which, on circulating, may result in dimensional problems inthe pieces obtained Likewise, with this type of additive, a reduction inthe mechanical resistance of the cores is produced.

Use of Titanium Oxide as an Additive

[0007] This new technique described in the U.S. Pat. No. 4,735,973, isbased on the use of titanium oxide additives, the additive being presentat percentages varying between 0.5 and 5% of the total amount of sandand said additive containing between 15 and 95% titanium oxide. Withthis technique, thermal expansion is reduced, preventing, as a result“veining”, maintaining the mechanical resistance of the cores and notproducing an increase in gas production. The disadvantage of thistechnique lies in the fact that the cores obtained possesses a certaintendency to penetration, it being necessary to apply paints or othertreatments on the surface of the cores obtained before proceeding tomelting the piece.

Use of Natural Sands of Low Expansion

[0008] This new technique uses for the formation of the core, specialsands of the rounded of sub-angular silica type, chromate sands,zirconium sands and olivine sands, which, due to their different degreesof thermal expansion, result in the reduction of “veining”, and even toits total elimination. The basic disadvantage of this technique is thehigh cost of this type of sand, with the consequent increase in the costto obtain the cores.

Use of Electrofused Sands of Low Expansion

[0009] According to this technique, the silica sand normally used forthe manufacture of cores is melted in electric ovens, until obtaining akind of paste without expansion capacity. Then, the paste obtained isground until obtaining a sand powder which is mixed approximately at 50%with silica sand. In this way, the expansion of the core is avoided,since the powder obtained from the silica paste does not have a capacityfor expansion and hence, neither produces fissures nor the correspondingveining. The basic disadvantage of this technique is the greatercomplexity of the production process, which makes the final cost toobtain the cores more expensive.

[0010] As may be appreciated, the techniques normally used to preventthe formation of “veining” consist either in the use of additives (ironoxide, titanium oxide, wood flours and coal powder) or in the use ofspecial sands (natural sands of low expansion or electrofused sands oflow expansion).

[0011] Now it has been found that it is possible to improve the qualityof the iron casting by using cores or molds manufactured with moldingsands incorporating hollow microspheres of aluminum silicate.

[0012] As a result, a purpose of this invention comprises a molding sandfor casting which incorporates hollow microspheres of aluminum silicate.

[0013] An additional purpose of this invention comprises a process tomanufacture cores or chill molds including the use of the molding sandindicated above. The resulting cores and molds also comprise a purposeof this invention.

[0014] Another additional purpose of this invention comprises a processto manufacture iron casting including the use of the cores or moldsmentioned above. The resulting iron casting also comprises a purpose ofthis invention.

SUMMARY OF THE INVENTION

[0015] The invention provides a molding sand for casting whichincorporates hollow microspheres of aluminum silicate in an amountbetween 1 and 30% by weight with respect to the total amount of moldingsand.

[0016] The molding sand, purpose of this invention, is suitable tomanufacture cores and chill molds which, in turn, may be used in themanufacture of iron casting.

[0017] The use of hollow microspheres of aluminum silicate prevents theappearance of fissures during core expansion, but without increasing gasproduction and maintaining the mechanical properties of the coreobtained. During melting of the piece, the expansion of the silica inthe molding sand does not cause an increase of the core, but theexpansion is absorbed by the internal spaces of the hollow microspheres,by which the appearance of fissures on the core surface is totallyprevented and, as a result, “veining”.

[0018] With the molding sand of the invention, cores or molds areobtained of lesser density, by which gas production is reduced, butwithout decreasing its mechanical resistance. Likewise, the penetrationof the piece obtained is reduced, due to the fact that the hollowmicrospheres of aluminum silicate cover the interstitial spaces of thecore producing an effect similar to that of paint, improving the surfaceof the piece obtained. Therefore, the quality of the resulting ironcasting is improved due to the reduction of the defects caused by coreexpansion and gas production.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 shows a bar diagram in which the “veining” effect is seenfor different techniques of core shaping, position 04 corresponding tothe technique based on the use of a molding sand of the inventioncontaining 10% by weight, of hollow microspheres of aluminum silicate.

[0020]FIG. 2 shows a bar diagram in which the mechanical resistanceobtained is seen according to the different techniques of coremanufacture, the position 04 corresponding to the technique based on theuse of a molding sand of the invention containing 10% by weight ofhollow microspheres of aluminum silicate.

[0021]FIG. 3 shows a bar diagram in which the density of the coresobtained is shown, according to the different manufacturing techniques.

[0022]FIG. 4 shows a comparative diagram of “veining” and penetrationobtained with molding sands containing hollow microspheres of aluminumsilicate (invention) and molding sands containing titanium oxideaccording the U.S. Pat. No. 4.735.973.

[0023]FIG. 5 shows a bar diagram in which the tensile strength of coresobtained with molding sands of this invention is shown, containingdifferent percentages of hollow microspheres of aluminum silicate, thecurves corresponding to the tensile strength at the exit of the box,after 24 hours and with a relative humidity of 100% being represented.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The invention provides a molding sand for casting incorporatinghollow microspheres of aluminum silicate at an amount between 1 and 30%by weight with respect to the total amount of sand, preferably between 5and 25% and more preferably, between 10 and 20%, by weight.

[0025] Preliminary tests intended to prevent the formation of “veining”on the iron casting surface showed the possibility of using hollowmicrospheres of aluminum silicate as an additive for molding sandsdestined to manufacture cores and chill molds.

[0026] Further tests permitted the verification that good results areobtained when the hollow microspheres of aluminum silicate used have analuminum content between 15 and 45% by weight, based on the weight ofthe hollow microspheres of aluminum silicate, preferably between 20 and35% by weight.

[0027] For their use in this invention, all kinds of hollow microspheresof aluminum silicate may be used, preferably those satisfying theaforementioned characteristics, such as those marketed by the PQCorporation under the trade mark Extendospheres, and those marketed byMicrofine Minerals Limited under the trade mark Metaspheres 50. In Table1, the main characteristics of the different microspheres used in thetests carried out are indicated.

[0028] Contrary to that expected, it was surprising to verify that thehollow microspheres of aluminum silicate of the best quality,understanding as such those microspheres with a relatively high aluminumcontent, typically between 35 and 45% by weight, give worse results thanwhen hollow microspheres of aluminum silicate of less quality are used,that is, with an aluminum content less than 35% by weight.

[0029] The tests performed with different hollow microspheres ofaluminum silicate, incorporated at different proportions to the moldingsand have shown that, surprisingly, the microspheres with a low contentin aluminum (25-33%) give, in general, the best results regarding“veining” and penetration, in turn maintaining the mechanical propertiesof the core obtained, moreover observing that an increase in thepercentage of aluminum in the microspheres does not imply an improvementin the results of said effects (“veining” and penetration), but, onoccasions, the opposite occurs [see Table 5, (Example 5)].

[0030] Moreover, the studies performed showed that the best resultsregarding veining and penetration do not only depend on the aluminumcontent, but other factors also have an influence, such as the size ofthe microspheres and the thickness of their walls. Particularly, it hasbeen observed that hollow microspheres of aluminum silicate are suitablehaving a wall thickness between 3 and 10% of the microsphere diameterand a particle size between 10 and 350 micrometers (μm).

[0031] As may be seen in Table 4 (example 4), the microspheres givingthe best results are those identified as Metaspheres 50 andExtendospheres SG, since they have a crushing strength of 189.37 kg/cm²(2.700 psi) with an aluminum content between 25 and 30% by weight, awall thickness of 5%, with respect to the particle diameter(Extendospheres SG) and from 3 to 7% with respect to the diameter of theparticle (Metaspheres 50), and an average particle size of 150 μm(Extendospheres SG) and between 10 and 250 μm (Metaspheres 50).

[0032] The molding sand of the invention may also contain otherconventional components, like casting aggregates, binders and otheroptional components used in this sector of the technique.

[0033] The invention also provides a process to manufacture a core orchill mold by means of a cold process comprising:

[0034] (A) introducing the molding sand, purpose of this invention, intoa mold to form a core or non-cured mold;

[0035] (B) placing said core or non-cured mold of stage (A) into contactwith a gaseous cured catalyst;

[0036] (C) permitting said core or non-cured mold resulting from stageB) to cure until said core or mold may be handled; and

[0037] (D) separating said core or mold from the mold.

[0038] In another embodiment, the invention also provides a process tomanufacture iron casting comprising:

[0039] (A) inserting the core or mold manufactured from the moldingsand, purpose of this invention, in a casting device;

[0040] (B) pouring the metal, in a liquid state, in said casting device;

[0041] (C) letting the metal poured into the casting

[0042] (D) separating the molten metal piece from the casting device.

[0043] The following examples serve to illustrate the invention. InTable 1, the main characteristics of the hollow microspheres of aluminumsilicate used in the execution of these examples are shown. TABLE 1Characteristics of different hollow microspheres of aluminum silicateAluminum Particle Crushing Softening content Wall size resistance pointProduct (%) thickness (μm) (kg/cm²) (° C.) Extendospheres 43, 3 = 10% Ø10-300 562, 48 1.800 SLG Extendospheres 43, 3 = 10% Ø 10-180 562, 481.800 SL180 Extendospheres 43, 3 = 10% Ø 10-150 562, 48 1.800 SL150Extendospheres 25-30 = 10% 10-300 189, 37 1.200- SG (radio) (media 130)1.350 Extendospheres 25-30 = 10% 10-350 189, 37 1.200- XEG (radio)(media 162) 1.350 Extendospheres 15 100 7, 03 1.000 XOL200 (media)Metaspheres 50 26-33 3-7% Ø 10-250 196, 8- 1.200- 1,968, 1 1.350

EXAMPLE 1 Study of the Use of Hollow Microspheres of Aluminum Silicateas an Additive For Molding Sands

[0044] To assess the possible use of hollow microspheres of aluminumsilicate as an additive for molding sands, destined to manufacturecasting cores, on the one hand some cores were formed using differentresins and conventional additives, and on the other hand, other coresfrom a molding sand, to which hollow microspheres of aluminum silicatehad been added, then studying “veining” and the tensile strength of thecores obtained. The techniques used to manufacture the different coreswere conventional for each case.

[0045] The distinctive components for the different mixtures used tomanufacture the cores, are summarized below (Table 2). In all the cases,2% resin was used. The catalyst used in preparation 02 and 03 was SO₂(gas) whilst in the remaining preparations, the catalyst used wasgaseous methylethylamine (DNEA). TABLE 2 Starting mixtures PreparationResin Molding sand 01 Phenolic Silica sand (*) urethane 02 Epoxy acrylicSilica sand (*) 03 Acrylic Silica sand (*) 04 Phenolic Silica sand (*) +10% hollow urethane microspheres of aluminum silicate (invention) 05Phenolic Recovered furanic sand urethane 06 Phenolic 70/30 silica sandurethane (*)/Chromite 07 Phenolic 50/50 silica sand urethane(*)/Chromite 08 Phenolic Silica sand (*) + 2% BR-022 urethane 09Phenolic Silica sand (*) + 2% coal urethane 10 Phenolic seggar clayurethane 11 Phenolic 50/50 electrofused silica urethane 12 Phenolictreated olivine urethane 13 Phenolic Thermally recovered sand urethane14 Phenolic Silica sand (*) + 10% Veinseal urethane 14000

[0046] Once the piece was prepared, the results were studied the value“10” to the maximum value of “veining” and a value “0” to the minimumvalue of “veining”. Besides “veining”, tensile strength was evaluated.

[0047] In FIGS. 1 and 2, bar diagrams are shown indicating the “veining”effect and tensile strength of the cores obtained. In the position 04,the properties obtained with the core obtained from molding sandcontaining microspheres of aluminum silicate at a percentage of 10% areshown, it being possible to observe the total absence of the “veining”effect and some good tensile strength properties

EXAMPLE 2 Density of Different Cores

[0048] The density of different cores obtained according to differentmanufacturing techniques has been determined including, for comparativepurposes, a core manufactured from a molding sand containing hollowmicrospheres of aluminum silicate, purpose of this invention. The cores,whose density has been evaluated were prepared using the sands andadditives listed below:

[0049] [1]: Additives of titanium oxide [U.S. Pat. No. 4,735,973](Veinseal).

[0050] [2]: Hollow microspheres of aluminum silicate (Invention).

[0051] [3]: Rounded silica.

[0052] [4]: Sub-angular silica.

[0053] [5]: 70/30 Rounded silica/chromite.

[0054] [6]: 90/10 Silica/Additive of titanium oxide [U.S. Pat. No.4,735,973] (Veinseal).

[0055] [7]: 90/10 Silica/Hollow microspheres of aluminum silicate(invention).

[0056] The results obtained are shown in FIG. 3, where it may beappreciated that the cores manufactured from molding sands containinghollow microspheres of aluminum silicate, have a very reduced densitywith respect to that of the other cores, a density permitting thereduction of gas production and penetration in the piece obtained.

EXAMPLE 3 Comparative Example

[0057] Some cores were prepared as from some molding sands containingdifferent amounts (0, 5%, 10% y 20%) of an additive selected between:

[0058] (i) hollow microspheres of aluminum silicate, and

[0059] (ii) additives of titanium oxide according to the North AmericanPatent U.S. Pat. No. 4,735,973 (Veinseal), and the effect of the same,both on “veining” and penetration has been evaluated.

[0060] The cores were prepared by mixing the sand (C-55) with 0.5%, 10%or 20% by weight of the additive in question and to the resultingmixtures, the suitable resins were added, formed and cured.

[0061] Once the different pieces were prepared, the results wereevaluated, giving the value “10” to the maximum level of “veining” andpenetration and the value “0” to the minimum level of “veining” andpenetration. To determine the penetration of the metal in the mold, thetest “Penetration 2×2 test casting” [AFS Transactions] was used, inwhich the cavities of the core in the test mold were visually examinedfor the existence of metal penetration.

[0062] The results obtained are shown in FIG. 4, where it is clearlyseen that the “veining” in both techniques is very similar and isgradually reduced until it disappears when the percentage of additivegradually increases until reaching 10%. However, the penetration usingadditives of titanium oxide increases as the percentage of additiveincreases, whilst when using hollow microspheres of aluminum silicate asan additive, the penetration remains constant and at a very reducedlevel.

EXAMPLE 4 Preparation of Cores Using Hollow Microspheres of AluminumSilicate as an Additive

[0063] Some cores were prepared (crushing trials) consisting of moldingsand, to which different amounts (0.5%, 10% and 20%) of hollowmicrospheres of aluminum silicate had been added, and the incidencethereof on the tensile strength of the cores obtained was evaluated.

[0064] The test pieces were prepared by mixing the sand (C-55) with0.5%, 10% or 20% by weight of some hollow microspheres of aluminumsilicate and to the resulting mixture, the appropriate resin mixture wasadded With the mixture obtained, the crushing trials were prepared whichwere cured with the suitable gas.

[0065] The results obtained are collected in FIG. 5, where the tensilestrength of the cores obtained with different percentages of theadditive, purpose of the invention, are shown, representing the curvescorresponding to the tensile strength at the exit of the box, after 24hours and with a relative humidity of 100%.

[0066] By means of a process similar to the above, some cores wereprepared as from the molding sands indicated in Table 3, obtained bymixing the sand (C-55) with 0.5%, 10% or 20% by weight of hollowmicrospheres of aluminum silicate. In all cases, 1% Isocure® 325(Ashland) resin and 1% Isocure® 625 (Ashland) resin, and DMEA as acatalyst were used. TABLE 3 Molding sands C-55 sand Additive Composition(% by weight) (% by weight) I 100   0 II 95  5 III 90 10 IV 80 20

[0067] The cores obtained were submitted to some abrasion resistancetests (Scratch Hardness, SH) and tensile strength tests (TensileHardness, TS). The results obtained are shown in Table 4. TABLE 4Mechanical resistances Resistance I II III IV composition TS SH TS SH TSSH TS SH 2 cc. 302 68 94 56 93 54 92 44 90  1 hour  76 95 72 94 74 96 6092 24 hours 88 99 95 97 98 97 85 96 1 h. Air 23 73 35 86 30 79 26 74 and24 h. 100% humidity Test piece 448.9 425.0 385.8 318.8 weight

[0068] The following examples were made with the purpose of selectingthe most suitable hollow microspheres of aluminum silicate for their useas an additive in molding sands.

EXAMPLE 5 Evaluation of Different Hollow Microspheres of AluminumSilicate as an “Anti-Veining” Additive

[0069] To evaluate the “anti-veining” behavior of different types ofmicrospheres of aluminum silicate, some test pieces for crushing testswere prepared, consisting of molding sand to which different amounts ofthe microspheres to be evaluated had been added.

[0070] The test pieces were prepared by mixing the sand (C-55) with 10%or 20% by weight of the microspheres and to the resulting mixture 0.75%Isocure® 325 (Ashland) and 0.75% Isocure® 625 (Ashland) were added. Withthe mixture obtained, some test pieces for crushing were made, gassingthem with Isocure® 720 (Ashland) Afterwards, they were placed in a moldfor their melting with gray iron at 1,420° C.

[0071] Once the piece had been cooled, the results were evaluated,giving the value “10” to the maximum level of “veining” and penetrationand the value “0” to the minimum level of “veining” and penetration. Todetermine the penetration of the metal in the mold, the test“Penetration 2×2 test casting” [AFS Transactions] was used, in which thecavities of the core were examined in the test mold to visually examinedthe existence of metal penetration.

[0072] The results obtained are shown in Table 5, where it may beappreciated that the best results regarding “veining” and penetration(that is, those in which “veining” and penetration was obtained with avalue of zero or very near to zero) were obtained when using 20% byweight of the hollow microspheres of aluminum silicate with an aluminumcontent between 25 and 33% (Extendospheres SG and Metaspheres SLG, SL180and SL150, with an aluminum content near to 45% by weight) which gavethe worse results in general. TABLE 5 Study of “anti-veining” productsTest pieces for crushing Isocure ® 325/ Isocure ® 625 (1.5% resin total)Test piece Test C-55 weight SL SL Meta. XOL piece No. sand (g) 180 150SLG 50 XEG SG 200 Veining Penetration Control A 100 175, 8 — 8 2  1  90151, 5 10 — — — — — — 9 2  2  80 122, 2 20 — — — — — — 9 2  3  90 150, 1— 10 — — — — — 9 2  4  80 124, 3 — 20 — — — — — 9 4  5  90 147, 2 — — 10— — — — 9 1  6  80 121, 0 — — 20 — — — — 10  0  7  90 150, 0 — — — 10 —— — 4 3  8  80 123, 2 — — — 20 — — — 0 0  9  90 144, 6 — — — — 10 — — 22 10  80 117, 0 — — — — 20 — — 0 1 11  90 147, 0 — — — — — 10 — 2 0 12 80 122, 0 — — — — — 20 — 0 0 13  90 175, 4 — — — — — — 10 9 2 14  95176, 0 — — — — — —  5 10  5

EXAMPLE 6 Evaluation of the Mechanical Resistance of “Anti-Veining”Additives

[0073] To evaluate the mechanical resistance of different types ofmicrospheres of aluminum silicate, some tensile strength test pieceswere prepared, consisting of sand to which different amounts of themicrospheres to he evaluated had been added.

[0074] The test pieces were prepared by mixing the sand (C-55) with 10%or 20% by weight of the microspheres and to the resulting mixture, 0.75%Isocure® 325 (Ashland) and 0.75% Isocure® 625 (Ashland) were added. Thecatalyst used was DMEA. With the mixture obtained, some tensile strengthtest pieces were made, which were subjected to abrasion resistance (SH)and tensile strength (TH) tests. The result obtained are shown in Table6, where it is observed that in spite of the good results obtained inthe “veining” and penetration effects, also satisfactory mechanicalresistances were obtained, for the cores prepared from the molding sandsof the invention. TABLE 6 Study of the mechanical resistances ofagglomerated products (sand/microspheres) ISOCURE ® 325 ISOCURE ® 325ISOCURE ® 325 ISOCURE ® 325 ISOCURE ® 325 ISOCURE ® 325 Resin ISOCURE ®625 ISOCURE ® 625 ISOCURE ® 625 ISOCURE ® 625 ISOCURE ® 625 ISOCURE ®625 Amount 1.5 1.5 1.5 1.5 1.5 1.5 Catalyst DMEA DMEA DMEA DMEA DMEADMEA Product 100% C-55 90% C-55 80% C-55 90% C-55 80% C-55 80% C-55Agglomerate (Control) 10% EX XEG 20% EX XEG 10% EX SG 20% EX SG 20% MS50 TS SH TS SH TS SH TS SH TS SH TS SH 3 cc. 3′ 50 92 67 92 56 90 63 9257 91 50 90 1 hour 73 96 72 94 58 91 70 93 59 93 48 73 24 hours 83 97 7894 63 92 86 95 73 95 66 87 1 h air & 24 h 60 94 61 89 59 90 70 93 60 9049 83 100% humidity Density 228.3 186.0 153.3 192.3 156.0 156.0 3 testpieces 6 hours of life in bank TS SH TS SH TS SH TS SH TS SH TS SH 3 cc.3′ 38 83 40 81 25 43 38 80 22 49 15 32 1 hour 46 91 44 83 26 44 40 82 2549 12 31 24 hours 55 94 48 86 30 47 48 85 29 50 13 40 1 h air & 24 h 4892 38 81 23 40 44 81 20 40 11 32 100% humidity

EXAMPLE 7 Evaluation of Mechanical Resistances of Different HollowMicrospheres of Aluminum Silicate

[0075] To evaluate the mechanical resistance of different hollowmicrospheres of aluminum silicate at 100%, some tensile strength testpieces were prepared, by mixing the microspheres (100%) to be evaluatedwith 3% Isocure® 323 (Ashland) and 3% Isocure® 623 (Ashland) With themixtures obtained, some tensile strength test pieces were made whichwere gassed with Isocure® 702 (Ashland) The test pieces obtained weresubmitted to abrasion resistance (SH) and tensile strength (TH) tests.The result obtained are shown in Table 7, where it may be appreciatedthat the best results were obtained with Extendospheres XEGmicrospheres, having an average particle size (162 μm) greater than theExtendospheres SG microspheres(130 μm). TABLE 7 Study of mechanicalresistances of different additives (with Isocure) used in themanufacture of sleeves METASPHERES EX SL180 EX SL150 EX SLG 50 EX SG EXXEG Microsphere ISOCURE ISOCURE ISOCURE ISOCURE ISOCURE ISOCURE Resin323/623 323/623 323/623 323/623 323/623 323/623 Resin amount 6 6 6 6 6 6Catalyst DMEA DMEA DMEA DMEA DMEA DMEA TS  SH TS  SH TS  SH TS  SH TS SH TS  SH 4 cc. 3′ 49  80 49  82 47  78 48  81 36  71 60  83 1 hour 63 86 52  84 66  87 43  80 50  80 66  83 24 hours 70  92 67  86 67  90 40 79 72  94 78  95 1 h air & 24 h 60  85 43  77 63  87 38  75 54  79 63 94 100% humidity

1. A molding sand for casting including hollow microspheres of aluminumsilicate.
 2. A sand, according to claim 1, wherein said hollowmicrospheres of aluminum silicate have an aluminum content between 15and 45% by weight, of the microspheres.
 3. A sand according to claim 2,wherein said hollow microspheres of aluminum silicate have an aluminumcontent between 20 and 35% by weight.
 4. A sand according to claim 1,wherein said hollow microspheres of aluminum silicate have a wallthickness between 3 and 10% of the microsphere diameter.
 5. A sandaccording to claim 1, wherein said hollow microspheres of aluminumsilicate have a particle size between 10 and 350 μm.
 6. A sand accordingto claim 1, comprising between 1 and 30% by weight of hollowmicrospheres of aluminum silicate, with respect to the total amount ofsand.
 7. A sand according to claim 6, comprising between 5 and 25% byweight of hollow microspheres of aluminum silicate with respect to thetotal amount of sand.
 8. A sand according to claim 7, comprising between10 and 20% by weight of hollow microspheres of aluminum silicate withrespect to the total amount of sand.
 9. A process to manufacture a coreor chill mold by means of cold process, comprising: (A) introducing amolding sand according to any of the claims 1 to 8, in a mold to form acore or non-cured mold; (B) putting said core or non-cured mold of thestage (A) in contact with a gaseous cured catalyst; (C) letting saidcore or non-cured mold resulting from the stage (B) cure until said coreor mold may be handled; and (D) separating said core or mold from themold.
 10. A core or chill mold prepared according to the process ofclaim
 9. 11. A process to manufacture iron casting, including: (A)inserting a core or chill mold, according to claim 10 in a castingdevice; (B) pouring the metal in a liquid state, in said casting device;(C) letting the metal poured into the casting device cool and solidify;and (D) separating the melted metal piece from the casting device. 12.An iron casting prepared according to the process of claim 11.